December 2008 4x4 Truck Tech Questions - Tech Line

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New Hummer Six-Speed ClunksQuestion: I own a new Hummer with the six-speed automatic transmission. I love the vehicle, but when I am in Drive and start out in First gear and then let up on the gas, there is this clunking noise either just before or just after the transmission shifts. My dealer says that this is normal, but it sure doesn't seem that it should make this kind of a noise.Jim AlbertonLos Angeles, CA

Answer: Your dealer service manager needs to look at GM Technical Service Bulletin No. 08-07-30-012, which covers this problem with the 6L80 six-speed automatic transmission. There is a revised transmission calibration that requires a reprogram of the Transmission Control Module that should solve your problem.

Using Snow Chains The Right WayQuestion: The other day, a couple of my buddies and I were talking about a snow trip we took where we had wished we had chains for our tires. I know that you live in Montana, which gets a lot of snow. My question is: If you only have one set of chains, should they go on the front or the back? Any other tips you have on using chains?John Phillipsvia fourwheeler.com

Answer: I am a California transplant to Montana, and in the 17 winters that I have been here, I've only put chains on my vehicles about three times. Where I lived in California, they got put on about 10 times each year. Why? Because driving conditions were a lot different. Montana does an excellent job of keeping the highways clear of snow. Some of the passes do get pretty nasty at times, and chains are then needed.

There have been a lot of tire technology changes in rubber compounds and tread design, which makes a difference in traction in both ice and snow. Besides that, the snow conditions are a bit different, and I only play in it with my vehicles when it's hard and firm, where flotation is the secret; not soft and slushy, where you have to dig through it. But that is really not the answer you're looking for, now is it?

I will give you the same answer that I gave a reader some 20 years ago and which I still find true. I prefer chains on the front tires. They're easier to install on the front because the wheelwell opening is generally bigger, and the wheel itself can be turned for better access to the inside hook if necessary. Putting them on the front also provides better steering and braking control. Most likely, better than 60 to 70 percent of stopping power is from the front wheels. If the front tires slide, steering is lost. You also get improved traction when going uphill as weight transfer causes the front tires to lose traction.

There are also some drawbacks to putting them up front. You will have to use four-wheel drive more often than if the chains were on the rear. On a downhill curve, the back end of the vehicle may want to slide outward and an oversteer condition exists. However, this can easily be corrected by a bit of throttle input and letting the front tires pull you back straight. With chains only on the back, there is a tendency for the front end to "push" (that is, not steering where you want it to go as the rear is doing most of the work).

When it comes to chains, buy the biggest, nastiest ones you can find. I always go oversize and cut the extra length off. I want the crossbars to come way down along the tire's sidewall. Not only do you gain some traction in deep snow, but the chains don't have the tendency to walk off the tire. I also double up on the crossbars. I found that this really makes a difference in traction. Put the chains on as tight as you can get the adjusters, and then drive a bit and retighten. I use heavy-duty commercial tarp tie-downs instead of cheap bungee cords or those silly excuses they sell for chain tensioners.

Explorer-To-XJ Axle Swap?Question: I recently purchased an '88 Jeep Cherokee Laredo with a small lift and 32x11.50s. I was driving home one day and the throttle stuck, so I shut it off and coasted it into my drive. Here is where the stupidity came in: I tried pulling it into gear to go up my drive, and in the long run tore up two spiders in the pinion gear. I know, dumb me.

I also have a '94 Ford Explorer XLT at my house and was wondering if I could use the rear axle out of that. I don't know what the gearing is on either of them-all I do know is they both have factory gears.Scotty B.via fourwheeler.com

Answer: The Ford Explorer differential has either 3.27:1s or optional 3.73:1s. The '88 XJ could have come with a 3.54:1, 3.73:1, 4.10:1, or 4.56:1 gear ratio. My books are not really clear here, but if I had to guess, it would be 3.54:1. If you're planning on using the Ford rearend, a gear change is maybe is order. It is important that both front and rear ratios match.

A quick way to find out the gear ratio is to place a mark on the tire and a corresponding mark on the ground. Also put a mark on the driveshaft opposite a reference point. Now push the vehicle forward one complete tire revolution and at the same time count the number of turns of the driveshaft. For example, if the driveshaft turns 31/2 times for every single rotation of the tires, then the gear ratio is 3.54:1.

I am not quite sure how one manages to break two spider gears by putting the transmission in gear, but then again, maybe they were damaged from another event and decided that it was now time to break-better in your driveway than on the trail. Seems to me it would be a lot easier to just replace the two spider gears than to swap rearends, as this involves moving the spring pads for proper alignment, and a new driveshaft. The wheel bolt pattern is the same, but you will find that the Ford is a bit narrower but usually doesn't cause any problems.

Now, there is an advantage to the Ford 8.8 in that you're getting a much stronger rear axle, but you will most likely have to build a new rear driveshaft and acquire a flange adapter to hook up the Spicer joint to the pinion flange.

Wants Grand Cherokee Rack InfoQuestion: Could you please tell what the part number is for the Olympic 4x4 rack you put in the back of "Ain't It Grand-er" Grand Cherokee project? Terry HawkinsMontrose, CO

Answer: The part number for the Olympic Mountaineer Rack is 907-154 (323/726-6988, www.olympic4x4products.com), and it fits both the ZJ Grand and the XJ Cherokee. You can find it in the Quadratec catalog or online at www.quadratec.com.

I couldn't be more pleased with the rack. At first I thought that I would only use it for trips as it takes less than a minute to remove. However, it has become so useful that it stays in all the time. The lower area offers great storage for things that may move around or come up and greet you in an accident, and the upper area is perfect for soft items like jackets and such.

AX-15 vs. NV3550: What's The Better Box?Question: I have a '99 Wrangler Sport with the Dana 44 rear (recently rebuilt), 3.73:1 gear ratio, and the 4.0L engine with about 84,000 miles now. The stock Aisin AX-15 transmission is starting to die on me (the synchronizers are wearing, making it nearly impossible to shift into Second, and Fourth gear grinds as I shift into it if done quickly). I am researching replacements/upgraded transmissions and see that an NV3550 will swap in easily. I have read some forums claiming the NV3550 is not a good swap, and that sticking with the AX-15 is the way to go. I'm hoping you can shed some light on this debate.Brian McCloskeyWashington, D.C.

Answer: First, I'm kind of surprised that you're having problems with the AX-15, as it has proven itself to be a pretty darn good transmission. I know an owner that has, like, 160,000 miles on his, and another owner who has run 220,000 on his without any problems. Before you swap transmissions, you might consider draining the present gear lube, and perhaps even running it though a strainer like a paint filter to see if there are any pieces or parts in the oil. Keep in mind, you're bound to find some small flakes of shining stuff, as that is just normal wear. Jeep specifications call for 77-90/GL3 gear lubricant, which is pretty standard.

Instead of a swap, I think that I would seriously consider having your local shop order one from a quality rebuilder such as All Trans in Portland. Yes, the 3550 is a very good replacement transmission, and most likely stronger than the AX-15, but when in Neutral-due to the design and clearances-it sounds like someone dropped a can full of rocks inside of it. From my experience, it is also not the best-shifting gearbox. Another choice would be Rockland Standard Gear's (www.rsgear.com/transmission.asp) new five-speed upgrade, appropriately called "The Terminator." It is a direct bolt-in replacement with more torque capacity for extreme duty.

Dodge V-10 Computer GremlinsQuestion: I bought an '01 Dodge 3/4-ton truck with the V-10 engine and the automatic transmission. It ran fine for several thousand miles, and now a problem has developed. Once in a while when I shift from Park to Drive, the engine will just stop running. I can put it back in Park and it will restart, and then be just fine for a few days. Any idea how I can fix this problem?Mark KentKansas City, KS

Answer: This I believe is a computer problem that Dodge had with several different models that used the V-10 engine. You're going to have to take the truck to your local dealer and have them reflash the engine's computer with a new code.

Pinpointing Explorer Driveline SquealQuestion: I own an '03 Ford Explorer that has a strange noise. It's kind of like a high-pitched squeal, and it varies in noise level as speed is increased or decreased. It started after I had the vehicle in for a transmission rebuild. I took it back to the transmission shop, and they say it is not coming from the transmission but the transfer case. They now want to rebuild the transfer case. Could they have done something to the transfer case when they took the transmission out to repair it?Jim OkleySacramento, CA

Answer: Yes, they could have, but I don't think that it is anything major. I believe your Explorer has a BorgWarner 44-11 transfer case which offers three different drive modes: full-time four-wheel drive, high-range, and low-range. On the transfer case are two speed sensors that relay driveshaft speed to the control module.

My guess is that they had one or both of the speed sensors out for some reason or another when they pulled the transmission out. It's easy to cock the speed sensors just a bit when reinstalling them, and the end result will be this high-pitched squealing noise you're hearing. Take the vehicle back and have them pull out the speed sensor, lube the O-ring really good, and reinstall it, making sure that it is flush with the case.

Turning An AWD Explorer Into A 4WDQuestion: I have a '99 Ford Explorer with a 5.0L and all-wheel drive. I want to lift it and put in a high/low transfer case. I want to try to keep the cost down, so I would like to use a Ford F-150 transfer case. I don't know want would work best and go in fairly easy. I have been a truck and coach mechanic for 10 years, so I am very handy and could make anything work-I just need a bit of help on what parts to look for on the transfer-case job.Travisvia fourwheeler.com

Answer: While at first it seems like a pretty easy swap, just pull out the present 44-03 and bolt in a manual-shift transfer case from a Ford F-150, it just may not be that easy or it may work out just fine. I talked to my transmission/transfer-case expert, Bob Hutchins of All Transmissions in Portland, Oregon, and he agreed. Ford also used in the Explorer a B-W 44-04 and 13-54 transfer case with a low-range; however, they both used an electric shift motor. No big thing, you say, just run a power lead connected to an on/off switch to the motor. But it just won't work like that. You see, Bob says that the electrical plug is a multiwire connector. Where do all these wires go? Well, to the computer, the antilock brake module, and a couple of sensors. Most likely, you're going to have a "check engine" light on all the time. But you don't have this wiring plug.

Bob says his books show a 13-54 in a manual-shift mode was also used in the Explorer, but I can't seem to find any reference to it. You have to go back a few years to when the F-150s were using the same 4R70W auto transmission as the Explorer and the 5.0L motor. They used a 44-06 manual shift or a 13-56 in electrical- or manual-shift configuration. My guess-and do keep in mind that it is just an educated guess-is that the transmission spline count as well as the length of the transmission's output shaft is the same for all the transfer cases, and the ones from the pickup should bolt right on. There should not be any electrical connections that you would have to worry about other than the plugs that send a signal to a "4WD/low range" indicator light. A warning light as such shouldn't be any problem to hook up. There also may be some variation in driveshaft length that would require new shafts to be made up. If it was my project, I would pull out the existing transfer case and make up a drawing of all the critical measurements and then go wrecking-yard hunting.

As to a lift over 4 inches not being available; it's because the halfshafts or drive-axle CV joints can't handle any more operational angle than what a 4-inch lift will cause. I would think that with a 4-inch lift you could use a 32-inch tire without any problems and most likely even a 33.

Dana 35 Axle UpgradesQuestion: I have a '98 Jeep Cherokee 4.0L with a Model 35 rearend. I need to rebuild it, but I'd like to upgrade it to allow a 4.5-inch suspension lift and 32-inch tires. My plans are to make this vehicle a daily driver that can go "play" on the weekends. Do you have any suggestions?Tim CortrechtCarmel, IN

Answer: I assume that you mean to rebuild the whole Jeep, not just the rearend. First off, don't even think about rebuilding the Dana 35. It is a notoriously bad axle to run with any tire size larger than stock. If you break an axleshaft, which you will in time, the remaining portion of the axleshaft, along with the wheel, will part company with the Jeep and leave you most likely stranded.

A couple of companies such as Alloy USA and Superior Axle & Gear sell a larger-diameter 30-spline high-strength axleshaft. However, it must be used with a special aftermarket locking differential such as sold by Detroit Locker. Last time I checked, the price was about $1,100, not including labor. OK, you gain axleshaft strength and a locker as well, but the axlehousing is a bit on the weak side, and I have seen several of them bend quite badly. I believe that someone does make a truss for it, but that is even more money.

I really think that the best bet is to swap it out for a Ford Explorer rear axle. They come with the larger-diameter axleshafts, a much larger ring-and-pinion gearset, and in either a 3.73:1 or 4.10:1 ratio. We made this swap in our "Project Ain't it Grand-er," which you can find on fourwheeler.com (under "project vehicles"), and while we had to convert the Ford rearend to coil springs, you would just have to relocate the spring pads as the Explorer uses leaf springs.

Now I question the fact that you say your '98 has a Dana 35 rear axle. I was under the impression that the '96-and-up Cherokees used what is referred to as the Chrysler 8.25 rearend with 29-spline axleshafts. It's easy to tell the difference between the two, as the rear Dana has a cover that looks similar to the cover on the front of your Jeep, while the Chrysler rearend cover is almost round and has a smooth face. This is a fairly decent rearend and should hold up well to a 32-inch tire.

If you do indeed have a 35 rearend, then another choice would be this Chrysler rearend, and it would be no harder to install than bolting it in place. Keep in mind that the '91-'95 Cherokees also used this Chrysler rearend but with a small axle spline count of 27 splines, which is not much better than the Dana 35.

You might also want to consider a Dana 44 out of a TJ, but this means that the coil-spring mounting brackets and such would have to be cut off and spring pads welded on. Whatever your final choice is, just be sure that the front and rear axle gear ratios match.

Now as to a complete rebuild of the Cherokee, the starting point can be anywhere you want it to be. There is a plethora of great suspension systems, tires, wheels, bumpers, and engine performance parts available for the Cherokee, a lot of which are advertised within the pages of this magazine. Have fun.

Building A Dodge 318 For Boggin'Question: I have a question for any of you old Dodge guys out there. I have an '83 Dodge Ramcharger (Prospector edition) that I have been using in the local mud races. I need to know if I should ditch the two-barrel intake and carb for a four-barrel instead. I'm running a 318 small-block with a set of Hooker headers. The engine has a lot of power and response, but recently I swapped my set of Super Sport 31x10.50/R15s for a set of Mud King 35x12.50R15s. I'm running 3.21:1 gears (stock ratio) and wonder if the four-barrel will give my old Dodge a little more torque.

This Ramcharger is also my weekend play toy, and I really don't want to make it into a full racer. I'm just trying to make an all-around good wheeler.Russell PetersonAfton, IA

Answer: I doubt that you are going to see much torque increase with the carb/manifold swap-at least, not enough to make the swap worthwhile at this time. What you really need to do is get rid of those 3.21:1 gears and get down in the 4.56:1 ratio. If your primary use is for mud racing, then an even lower gear may be better. The swap to the 35-inch tires killed your overall gear ratio, making it equal to having about a 2.90:1 ratio. The lower gearing will put the rpm into a range where your engine will be making better horsepower and torque a lot quicker when making you run down the track.

When the gearing has been changed, then you should consider making the carb/manifold swap along with headers and a low-restriction exhaust system. One of the mistakes people make when doing a carb/manifold swap is to think that bigger is better. This is generally not so unless you have a full-out racing engine. Keep the carb in the 600-cfm range, and make sure you buy a manifold that matches the rpm range of the engine. You might want to consider one of Edelbrock's Performer packages that include a camshaft change as a starting point.